Laser light used to cool object to quantum ground state

ScienceDaily (Oct. 9, 2011) — For the first time, researchers at the California Institute of Technology (Caltech), in collaboration with a team from the University of Vienna, have managed to cool a miniature mechanical object to its lowest possible energy state using laser light. The achievement paves the way for the development of exquisitely sensitive detectors as well as for quantum experiments that scientists have long dreamed of conducting.

"We've taken a solid mechanical system -- one made up of billions of atoms -- and used optical light to put it into a state in which it behaves according to the laws of quantum mechanics. In the past, this has only been achieved with trapped single atoms or ions," says Oskar Painter, professor of applied physics and executive officer for applied physics and materials science at Caltech and the principal investigator on a paper describing the work that appears in the October 6 issue of the journal Nature.

As described in the paper, Painter and his colleagues have engineered a nanoscale object -- a tiny mechanical silicon beam -- such that laser light of a carefully selected frequency can enter the system and, once reflected, can carry thermal energy away, cooling the system.

By carefully designing each element of the beam as well as a patterned silicon shield that isolates it from the environment, Painter and colleagues were able to use the laser cooling technique to bring the system down to the quantum ground state, where mechanical vibrations are at an absolute minimum. Such a cold mechanical object could help detect very small forces or masses, whose presence would normally be masked by the noisy thermal vibrations of the sensor.

"In many ways, the experiment we've done provides a starting point for the really interesting quantum-mechanical experiments one wants to do," Painter says. For example, scientists would like to show that a mechanical system could be coaxed into a quantum superposition -- a bizarre quantum state in which a physical system can exist in more than one position at once. But they need a system at the quantum ground state to begin such experiments.

To reach the ground state, Painter's group had to cool its mechanical beam to a temperature below 100 millikelvin (-273.15°C). That's because the beam is designed to vibrate at gigahertz frequencies (corresponding to a billion cycles per second) -- a range where a large number of phonons are present at room temperature. Phonons are the most basic units of vibration just as the most basic units or packets of light are called photons. All of the phonons in a system have to be removed to cool it to the ground state.

Conventional means of cryogenically cooling to such temperatures exist but require expensive and, in some cases, impractical equipment. There's also the problem of figuring out how to measure such a cold mechanical system. To solve both problems, the Caltech team used a different cooling strategy.

"What we've done is used the photons -- the light field -- to extract phonons from the system," says Jasper Chan, lead author of the new paper and a graduate student in Painter's group. To do so, the researchers drilled tiny holes at precise locations in their mechanical beam so that when they directed laser light of a particular frequency down the length of the beam, the holes acted as mirrors, trapping the light in a cavity and causing it to interact strongly with the mechanical vibrations of the beam.

Because a shift in the frequency of the light is directly related to the thermal motion of the mechanical object, the light -- when it eventually escapes from the cavity -- also carries with it information about the mechanical system, such as the motion and temperature of the beam. Thus, the researchers have created an efficient optical interface to a mechanical element -- or an optomechanical transducer -- that can convert information from the mechanical system into photons of light.

Importantly, since optical light, unlike microwaves or electrons, can be transmitted over large, kilometer-length distances without attenuation, such an optomechanical transducer could be useful for linking different quantum systems -- a microwave system with an optical system, for example. While Painter's system involves an optical interface to a mechanical element, other teams have been developing systems that link a microwave interface to a mechanical element. What if those two mechanical elements were the same? "Then," says Painter, "I could imagine connecting the microwave world to the optical world via this mechanical conduit one photon at a time."

The Caltech team isn't the first to cool a nanomechanical object to the quantum ground state; a group led by former Caltech postdoctoral scholar Andrew Cleland, now at the University of California, Santa Barbara, accomplished this in 2010 using more conventional refrigeration techniques, and, earlier this year, a group from the National Institute of Standards and Technology in Boulder, Colorado, cooled an object to the ground state using microwave radiation. The new work, however, is the first in which a nanomechanical object has been put into the ground state using optical light.

"This is an exciting development because there are so many established techniques for manipulating and measuring the quantum properties of systems using optics," Painter says.

The other cooling techniques used starting temperatures of approximately 20 millikelvin -- more than a factor of 10,000 times cooler than room temperature. Ideally, to simplify designs, scientists would like to initiate these experiments at room temperature. Using laser cooling, Painter and his colleagues were able to perform their experiment at a much higher temperature -- only about 10 times lower than room temperature.

The work was supported by Caltech's Kavli Nanoscience Institute; the Defense Advanced Research Projects Agency's Microsystems Technology Office through a grant from the Air Force Office of Scientific Research; the European Commission; the European Research Council; and the Austrian Science Fund.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by California Institute of Technology, via EurekAlert!, a service of AAAS.

Journal Reference:

Jasper Chan, T. P. Mayer Alegre, Amir H. Safavi-Naeini, Jeff T. Hill, Alex Krause, Simon Gröblacher, Markus Aspelmeyer, Oskar Painter. Laser cooling of a nanomechanical oscillator into its quantum ground state. Nature, 2011; 478 (7367): 89 DOI: 10.1038/nature10461

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Laser light used to cool object to quantum ground state

ScienceDaily (Oct. 9, 2011) — For the first time, researchers at the California Institute of Technology (Caltech), in collaboration with a team from the University of Vienna, have managed to cool a miniature mechanical object to its lowest possible energy state using laser light. The achievement paves the way for the development of exquisitely sensitive detectors as well as for quantum experiments that scientists have long dreamed of conducting.

"We've taken a solid mechanical system -- one made up of billions of atoms -- and used optical light to put it into a state in which it behaves according to the laws of quantum mechanics. In the past, this has only been achieved with trapped single atoms or ions," says Oskar Painter, professor of applied physics and executive officer for applied physics and materials science at Caltech and the principal investigator on a paper describing the work that appears in the October 6 issue of the journal Nature.

As described in the paper, Painter and his colleagues have engineered a nanoscale object -- a tiny mechanical silicon beam -- such that laser light of a carefully selected frequency can enter the system and, once reflected, can carry thermal energy away, cooling the system.

By carefully designing each element of the beam as well as a patterned silicon shield that isolates it from the environment, Painter and colleagues were able to use the laser cooling technique to bring the system down to the quantum ground state, where mechanical vibrations are at an absolute minimum. Such a cold mechanical object could help detect very small forces or masses, whose presence would normally be masked by the noisy thermal vibrations of the sensor.

"In many ways, the experiment we've done provides a starting point for the really interesting quantum-mechanical experiments one wants to do," Painter says. For example, scientists would like to show that a mechanical system could be coaxed into a quantum superposition -- a bizarre quantum state in which a physical system can exist in more than one position at once. But they need a system at the quantum ground state to begin such experiments.

To reach the ground state, Painter's group had to cool its mechanical beam to a temperature below 100 millikelvin (-273.15°C). That's because the beam is designed to vibrate at gigahertz frequencies (corresponding to a billion cycles per second) -- a range where a large number of phonons are present at room temperature. Phonons are the most basic units of vibration just as the most basic units or packets of light are called photons. All of the phonons in a system have to be removed to cool it to the ground state.

Conventional means of cryogenically cooling to such temperatures exist but require expensive and, in some cases, impractical equipment. There's also the problem of figuring out how to measure such a cold mechanical system. To solve both problems, the Caltech team used a different cooling strategy.

"What we've done is used the photons -- the light field -- to extract phonons from the system," says Jasper Chan, lead author of the new paper and a graduate student in Painter's group. To do so, the researchers drilled tiny holes at precise locations in their mechanical beam so that when they directed laser light of a particular frequency down the length of the beam, the holes acted as mirrors, trapping the light in a cavity and causing it to interact strongly with the mechanical vibrations of the beam.

Because a shift in the frequency of the light is directly related to the thermal motion of the mechanical object, the light -- when it eventually escapes from the cavity -- also carries with it information about the mechanical system, such as the motion and temperature of the beam. Thus, the researchers have created an efficient optical interface to a mechanical element -- or an optomechanical transducer -- that can convert information from the mechanical system into photons of light.

Importantly, since optical light, unlike microwaves or electrons, can be transmitted over large, kilometer-length distances without attenuation, such an optomechanical transducer could be useful for linking different quantum systems -- a microwave system with an optical system, for example. While Painter's system involves an optical interface to a mechanical element, other teams have been developing systems that link a microwave interface to a mechanical element. What if those two mechanical elements were the same? "Then," says Painter, "I could imagine connecting the microwave world to the optical world via this mechanical conduit one photon at a time."

The Caltech team isn't the first to cool a nanomechanical object to the quantum ground state; a group led by former Caltech postdoctoral scholar Andrew Cleland, now at the University of California, Santa Barbara, accomplished this in 2010 using more conventional refrigeration techniques, and, earlier this year, a group from the National Institute of Standards and Technology in Boulder, Colorado, cooled an object to the ground state using microwave radiation. The new work, however, is the first in which a nanomechanical object has been put into the ground state using optical light.

"This is an exciting development because there are so many established techniques for manipulating and measuring the quantum properties of systems using optics," Painter says.

The other cooling techniques used starting temperatures of approximately 20 millikelvin -- more than a factor of 10,000 times cooler than room temperature. Ideally, to simplify designs, scientists would like to initiate these experiments at room temperature. Using laser cooling, Painter and his colleagues were able to perform their experiment at a much higher temperature -- only about 10 times lower than room temperature.

The work was supported by Caltech's Kavli Nanoscience Institute; the Defense Advanced Research Projects Agency's Microsystems Technology Office through a grant from the Air Force Office of Scientific Research; the European Commission; the European Research Council; and the Austrian Science Fund.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by California Institute of Technology, via EurekAlert!, a service of AAAS.

Journal Reference:

Jasper Chan, T. P. Mayer Alegre, Amir H. Safavi-Naeini, Jeff T. Hill, Alex Krause, Simon Gröblacher, Markus Aspelmeyer, Oskar Painter. Laser cooling of a nanomechanical oscillator into its quantum ground state. Nature, 2011; 478 (7367): 89 DOI: 10.1038/nature10461

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Planet-sized object as cool as Earth revealed in record-breaking photo

ScienceDaily (Oct. 19, 2011) — The photo of a nearby star and its orbiting companion -- whose temperature is like a hot summer day in Arizona -- will be presented by Penn State Associate Professor of Astronomy and Astrophysics Kevin Luhman during the Signposts of Planets conference at NASA's Goddard Space Flight Center on Oct. 20, 2011.

A paper describing the discovery will be published in the Astrophysical Journal.

"This planet-like companion is the coldest object ever directly photographed outside our solar system," said Luhman, who led the discovery team. "Its mass is about the same as many of the known extra-solar planets -- about six to nine times the mass of Jupiter -- but in other ways it is more like a star. Essentially, what we have found is a very small star with an atmospheric temperature about cool as the Earth's."

Luhman classifies this object as a "brown dwarf," an object that formed just like a star out of a massive cloud of dust and gas. But the mass that a brown dwarf accumulates is not enough to ignite thermonuclear reactions in its core, resulting in a failed star that is very cool. In the case of the new brown dwarf, the scientists have gauged the temperature of its surface to be between 80 and 160 degrees Fahrenheit -- possibly as cool as a human.

Ever since brown dwarfs first were discovered in 1995, astronomers have been trying to find new record holders for the coldest brown dwarfs because these objects are valuable as laboratories for studying the atmospheres of planets with Earth-like temperatures outside our solar system.

Astronomers have named the brown dwarf "WD 0806-661 B" because it is the orbiting companion of an object named "WD 0806-661" -- the "white dwarf" core of a star that was like the Sun until its outer layers were expelled into space during the final phase of its evolution. "The distance of this white dwarf from the Sun is 63 light years, which is very near our solar system compared with most stars in our galaxy," Luhman said.

"The distance of this white dwarf from its brown-dwarf companion is 2500 astronomical units (AU) -- about 2500 times the distance between the Earth and the Sun, so its orbit is very large as compared with the orbits of planets, which form within a disk of dust swirling close around a newborn star," said Adam Burgasser at the University of California, San Diego, a member of the discovery team. Because it has such a large orbit, the astronomers say this companion most probably was born in the same manner as binary stars, which are known to be separated as far apart as this pair, while remaining gravitationally bound to each other.

Luhman and his colleagues presented this new candidate for the coldest known brown dwarf in a paper published in spring 2011, and they now have confirmed its record-setting cool temperature in a new paper that will be published in the Astrophysical Journal.

To make their discovery, Luhman and his colleagues searched through infrared images of over six hundred stars near our solar system. They compared images of nearby stars taken a few years apart, searching for any faint points of light that showed the same motion across the sky as the targeted star. "Objects with cool temperatures like the Earth are brightest at infrared wavelengths," Luhman said. "We used NASA's Spitzer Space Telescope because it is the most sensitive infrared telescope available."

Luhman and his team discovered the brown dwarf WD 0806-661 B moving in tandem with the white dwarf WD 0806-661 in two Spitzer images taken in 2004 and 2009. The images, which together show the movement of the objects, are available online (http://science.psu.edu/alert/photos/research-photos/astro/Luhman-moving-labels.gif). "This animation is a fun illustration of our technique because it resembles the method used to discovery Pluto in our own solar system," Luhman said.

In a related new discovery involving a different cool brown dwarf, Penn State Postdoctoral Scholar John Bochanski and his colleagues have made the most detailed measurement yet of ammonia in the atmosphere of an object outside our solar system. "These new data are much higher quality that previously achieved, making it possible to study, in much more detail than ever before, the atmospheres of the coldest brown dwarfs, which most closely resemble the atmospheres that are possible around planets," Bochanski said.

"Brown dwarfs that are far from their companion stars are much easier to study than are planets, which typically are difficult to observe because they get lost in the glare of the stars they orbit," Burgasser said. "Brown dwarfs with Earth-like temperatures allow us to refine theories about the atmospheres of objects outside our solar system that have comparatively cool atmospheres like that of our own planet."

This research was sponsored by grants from the National Science Foundation and the NASA Astrophysics Theory Program.

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